Method for parameter set reference contraints in coded video stream

ABSTRACT

There is included a method and apparatus comprising computer code configured to cause a processor or processors to perform obtaining video data comprising data of a plurality of semantically independent source pictures, determining, among the video data, whether references are associated with any of a first access unit (AU) and a second AU according to at least one picture order count (POC) signal value included with the video data, and outputting a first quantity of the references set to the first AU and a second quantity of the references set to the second AU based on the at least one POC signal value.

CROSS-REFERENCES TO RELATED APPLICATIONS/PRIORITY CLAIM

The present application is a continuation of U.S. Ser. No. 17/063,085,filed Oct. 5, 2020, which claims priority to provisional applicationU.S. 62/954,883 filed on Dec. 30, 2019, the entire contents of each ofwhich being hereby expressly incorporated by reference, in theirentireties, into the present application.

FIELD

The disclosed subject matter relates to video coding and decoding, andmore specifically according to exemplary embodiments, to a parameter setreference and scope in a coded video stream.

BACKGROUND

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video canconsist of a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in MPEG-2, system designs areknown to change the horizontal resolution (and, thereby, the picturesize) dependent on factors such as activity of the scene, but only at Ipictures, hence typically for a GOP. The resampling of referencepictures for use of different resolutions within a CVS is known, forexample, from ITU-T Rec. H.263 Annex P. However, here the picture sizedoes not change, only the reference pictures are being resampled,resulting potentially in only parts of the picture canvas being used (incase of downsampling), or only parts of the scene being captured (incase of upsampling). Further, H.263 Annex Q allows the resampling of anindividual macroblock by a factor of two (in each dimension), upward ordownward. Again, the picture size remains the same. The size of amacroblock is fixed in H.263, and therefore does not need to besignaled.

Changes of picture size in predicted pictures became more mainstream inmodern video coding. For example, VP9 allows reference pictureresampling and change of resolution for a whole picture. Similarly,certain proposals made towards VVC (including, for example, Hendry, et.al, “On adaptive resolution change (ARC) for VVC”, Joint Video Teamdocument WET-M0135-v1, Jan. 9-19, 2019, incorporated herein in itsentirety) allow for resampling of whole reference pictures todifferent—higher or lower—resolutions. In that document, differentcandidate resolutions are suggested to be coded in the sequenceparameter set and referred to by per-picture syntax elements in thepicture parameter set.

Compressed domain aggregation or extraction of multiple semanticallyindependent picture parts into a single video picture has gained someattention. In particular, in the context of, for example, 360 coding orcertain surveillance applications, multiple semantically independentsource pictures (for examples the six cube surface of a cube-projected360 scene, or individual camera inputs in case of a multi-camerasurveillance setup) may require separate adaptive resolution settings tocope with different per-scene activity at a given point in time.

SUMMARY

Disclosed are techniques for signaling of adaptive picture size in avideo bitstream.

There is included a method and apparatus comprising memory configured tostore computer program code and a processor or processors configured toaccess the computer program code and operate as instructed by thecomputer program code. The computer program includes obtaining codeconfigured to cause the at least one processor to obtain video datacomprising data of a plurality of semantically independent sourcepictures, determining code configured to cause the at least oneprocessor to determine, among the video data, whether references areassociated with any of a first access unit (AU) and a second AUaccording to at least one picture order count (POC) signal valueincluded with the video data, and outputting code configured to causethe at least one processor to output a first quantity of the referencesset to the first AU and a second quantity of the references set to thesecond AU based on the at least one POC signal value.

According to exemplary embodiments, the references comprise at least oneof pictures, slices, and tiles of the video data.

According to exemplary embodiments, determining whether the referencesare associated with any of the first AU and the second AU comprisescomparing respective POC values of each of the references with the atleast one POC signal value.

According to exemplary embodiments, determining whether the referencesare associated with any of the first AU and the second AU furthercomprises setting the first quantity of the references to the first AU,in response to determining that each of the first quantity of thereferences respectively comprises one of a plurality of POC values lessthan the at least one POC signal value, and setting the second quantityof the references to the second AU, in response to determining that eachof the second quantity of the references respectively comprises one of asecond plurality of POC values equal to or greater than the at least onePOC signal value,

According to exemplary embodiments, the references comprise the slices,and the at least one POC signal value is included in a slice header ofthe video data.

According to exemplary embodiments, the video data comprises a videoparameter set (VPS) data identifying a plurality of spatial layers ofthe video data.

According to exemplary embodiments, the at least one POC signal value isincluded in the video parameter set (VPS) of the video data.

According to exemplary embodiments, the determining code is furtherconfigured to cause the at least one processor to determine whether theVPS data comprises at least one flag indicating whether one or more ofthe references are divided into a plurality of sub-regions and todetermine, in a case where the at least one flag indicates that the oneor more of the references are divided into the plurality of sub-regions,at least one of, in luma samples, a full picture width and a fullpicture height of a picture of the one or more of the references.

According to exemplary embodiments, the determining code is furtherconfigured to cause the at least one processor to determine, in the casewhere the at least one flag indicates that the one or more of thereferences are divided into the plurality of sub-regions, a signalingvalue, included in a sequence parameter set of the video data,specifying an offset of a portion of at least one of the sub-regions.

According to exemplary embodiments, the plurality of semanticallyindependent source pictures represent a spherical 360 picture.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIGS. 5A and 5B are schematic illustrations of options for signaling ARCparameters in accordance with prior art or an embodiment, as indicated.

FIG. 6 is an example of a syntax table in accordance with an embodiment.

FIG. 7 is a schematic illustration of a computer system in accordancewith an embodiment.

FIG. 8 is an example of prediction structure for scalability withadaptive resolution change.

FIG. 9 is an example of a syntax table in accordance with an embodiment.

FIG. 10 is a schematic illustration of a simplified block diagram ofparsing and decoding picture order count (POC) cycle per access unit andaccess unit count value.

FIG. 11 is a schematic illustration of a video bitstream structurecomprising multi-layered sub-pictures.

FIG. 12 is a schematic illustration of a display of the selectedsub-picture with an enhanced resolution.

FIG. 13 is a block diagram of the decoding and display process for avideo bitstream comprising multi-layered sub-pictures.

FIG. 14 is a schematic illustration of 360 video display with anenhancement layer of a sub-picture.

FIG. 15 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure.

FIG. 16 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, with spatialscalability modality of local region.

FIG. 17 is an example of a syntax table for sub-picture layoutinformation

FIG. 18 is an example of a syntax table of SEI message for sub-picturelayout information.

FIG. 19 is an example of a syntax table to indicate output layers andprofile/tier/level information for each output layer set.

FIG. 20 is an example of a syntax table to indicate output layer mode onfor each output layer set.

FIG. 21 is an example of a syntax table to indicate the presentsubpicture of each layer for each output layer set.

FIG. 22 is an example of parameter set reference in a non-referencelayer.

PROBLEM TO BE SOLVED

As compressed domain aggregation or extraction of multiple semanticallyindependent picture parts into a single video picture has gained someattention, in the context of, for example, 360 coding or certainsurveillance applications, multiple semantically independent sourcepictures (for examples the six cube surface of a cube-projected 360scene, or individual camera inputs in case of a multi-camerasurveillance setup) may require separate adaptive resolution settings tocope with different per-scene activity at a given point in time.Therefore, there is disclosed herein, among other things, encoders, at agiven point in time, that may choose to use different resampling factorsfor different semantically independent pictures that make up the whole360 or surveillance scene. When combined into a single picture, that, inturn, requires that reference picture resampling is performed, andadaptive resolution coding signaling is available, for parts of a codedpicture.

DETAILED DESCRIPTION

FIG. 1 illustrates a simplified block diagram of a communication system100 according to an embodiment of the present disclosure. The system 100may include at least two terminals 110 and 120 interconnected via anetwork 150. For unidirectional transmission of data, a first terminal110 may code video data at a local location for transmission to theother terminal 120 via the network 150. The second terminal 120 mayreceive the coded video data of the other terminal from the network 150,decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals 130, 140 provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal 130, 140 may code video data captured at a locallocation for transmission to the other terminal via the network 150.Each terminal 130, 140 also may receive the coded video data transmittedby the other terminal, may decode the coded data and may display therecovered video data at a local display device.

In FIG. 1, the terminals 110, 120, 130, 140 may be illustrated asservers, personal computers and smart phones but the principles of thepresent disclosure may be not so limited. Embodiments of the presentdisclosure find application with laptop computers, tablet computers,media players and/or dedicated video conferencing equipment. The network150 represents any number of networks that convey coded video data amongthe terminals 110, 120, 130, 140, including for example wireline and/orwireless communication networks. The communication network 150 mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network 150may be immaterial to the operation of the present disclosure unlessexplained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem 213, that can includea video source 201, for example a digital camera, creating a for exampleuncompressed video sample stream 202. That sample stream 202, depictedas a bold line to emphasize a high data volume when compared to encodedvideo bitstreams, can be processed by an encoder 203 coupled to thecamera 201. The encoder 203 can include hardware, software, or acombination thereof to enable or implement aspects of the disclosedsubject matter as described in more detail below. The encoded videobitstream 204, depicted as a thin line to emphasize the lower datavolume when compared to the sample stream, can be stored on a streamingserver 205 for future use. One or more streaming clients 206, 208 canaccess the streaming server 205 to retrieve copies 207, 209 of theencoded video bitstream 204. A client 206 can include a video decoder210 which decodes the incoming copy of the encoded video bitstream 207and creates an outgoing video sample stream 211 that can be rendered ona display 212 or other rendering device (not depicted). In somestreaming systems, the video bitstreams 204, 207, 209 can be encodedaccording to certain video coding/compression standards. Examples ofthose standards include ITU-T Recommendation H.265. Under development isa video coding standard informally known as Versatile Video Coding orVVC. The disclosed subject matter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder 210according to an embodiment of the present invention.

A receiver 310 may receive one or more codec video sequences to bedecoded by the decoder 210; in the same or another embodiment, one codedvideo sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel 312, which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver 310 may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver 310 may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory 315 may be coupled inbetween receiver 310 and entropy decoder/parser 320 (“parser”henceforth). When receiver 310 is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer 315 may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer 315 may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder 210 may include an parser 320 to reconstruct symbols321 from the entropy coded video sequence. Categories of those symbolsinclude information used to manage operation of the decoder 210, andpotentially information to control a rendering device such as a display212 that is not an integral part of the decoder but can be coupled toit, as was shown in FIG. 2. The control information for the renderingdevice(s) may be in the form of Supplementary Enhancement Information(SEI messages) or Video Usability Information (VUI) parameter setfragments (not depicted). The parser 320 may parse/entropy-decode thecoded video sequence received. The coding of the coded video sequencecan be in accordance with a video coding technology or standard, and canfollow principles well known to a person skilled in the art, includingvariable length coding, Huffman coding, arithmetic coding with orwithout context sensitivity, and so forth. The parser 320 may extractfrom the coded video sequence, a set of subgroup parameters for at leastone of the subgroups of pixels in the video decoder, based upon at leastone parameters corresponding to the group. Subgroups can include Groupsof Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units(CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and soforth. The entropy decoder/parser may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser 320 may perform entropy decoding/parsing operation on thevideo sequence received from the buffer 315, so to create symbols 321.

Reconstruction of the symbols 321 can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser 320. The flow of such subgroup control information between theparser 320 and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit 351. Thescaler/inverse transform unit 351 receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) 321 from the parser 320. It can output blockscomprising sample values, that can be input into aggregator 355.

In some cases, the output samples of the scaler/inverse transform 351can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit 352 generates a block of the same size and shape of theblock under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture 356.The aggregator 355, in some cases, adds, on a per sample basis, theprediction information the intra prediction unit 352 has generated tothe output sample information as provided by the scaler/inversetransform unit 351.

In other cases, the output samples of the scaler/inverse transform unit351 can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit 353 canaccess reference picture memory 357 to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols 321 pertaining to the block, these samples can be addedby the aggregator 355 to the output of the scaler/inverse transform unit(in this case called the residual samples or residual signal) so togenerate output sample information. The addresses within the referencepicture memory form where the motion compensation unit fetchesprediction samples can be controlled by motion vectors, available to themotion compensation unit in the form of symbols 321 that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory when sub-sample exact motion vectors are in use, motionvector prediction mechanisms, and so forth.

The output samples of the aggregator 355 can be subject to various loopfiltering techniques in the loop filter unit 356. Video compressiontechnologies can include in-loop filter technologies that are controlledby parameters included in the coded video bitstream and made availableto the loop filter unit 356 as symbols 321 from the parser 320, but canalso be responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit 356 can be a sample stream that canbe output to the render device 212 as well as stored in the referencepicture memory 356 for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser 320), the current reference picture 356can become part of the reference picture buffer 357, and a fresh currentpicture memory can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder 320 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver 310 may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder 320 to properly decode the data and/or to more accuratelyreconstruct the original video data. Additional data can be in the formof, for example, temporal, spatial, or SNR enhancement layers, redundantslices, redundant pictures, forward error correction codes, and so on.

FIG. 4 may be a functional block diagram of a video encoder 203according to an embodiment of the present disclosure.

The encoder 203 may receive video samples from a video source 201 (thatis not part of the encoder) that may capture video image(s) to be codedby the encoder 203.

The video source 201 may provide the source video sequence to be codedby the encoder 203 in the form of a digital video sample stream that canbe of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, . . .), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source 201 may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source 203 may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focusses on samples.

According to an embodiment, the encoder 203 may code and compress thepictures of the source video sequence into a coded video sequence 443 inreal time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofcontroller 450. Controller 450 controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller 450 as they may pertain to video encoder 203 optimized fora certain system design.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder 430 (“sourcecoder” henceforth) (responsible for creating symbols based on an inputpicture to be coded, and a reference picture(s)), and a (local) decoder433 embedded in the encoder 203 that reconstructs the symbols to createthe sample data a (remote) decoder also would create (as any compressionbetween symbols and coded video bitstream is lossless in the videocompression technologies considered in the disclosed subject matter).That reconstructed sample stream is input to the reference picturememory 434. As the decoding of a symbol stream leads to bit-exactresults independent of decoder location (local or remote), the referencepicture buffer content is also bit exact between local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is well known to a person skilled in the art.

The operation of the “local” decoder 433 can be the same as of a“remote” decoder 210, which has already been described in detail abovein conjunction with FIG. 3. Briefly referring also to FIG. 3, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder 445 and parser 320 can be lossless, theentropy decoding parts of decoder 210, including channel 312, receiver310, buffer 315, and parser 320 may not be fully implemented in localdecoder 433.

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focusses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder 430 may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine 432 codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder 433 may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder 430. Operations of the coding engine 432 may advantageouslybe lossy processes. When the coded video data may be decoded at a videodecoder (not shown in FIG. 4), the reconstructed video sequencetypically may be a replica of the source video sequence with someerrors. The local video decoder 433 replicates decoding processes thatmay be performed by the video decoder on reference frames and may causereconstructed reference frames to be stored in the reference picturecache 434. In this manner, the encoder 203 may store copies ofreconstructed reference frames locally that have common content as thereconstructed reference frames that will be obtained by a far-end videodecoder (absent transmission errors).

The predictor 435 may perform prediction searches for the coding engine432. That is, for a new frame to be coded, the predictor 435 may searchthe reference picture memory 434 for sample data (as candidate referencepixel blocks) or certain metadata such as reference picture motionvectors, block shapes, and so on, that may serve as an appropriateprediction reference for the new pictures. The predictor 435 may operateon a sample block-by-pixel block basis to find appropriate predictionreferences. In some cases, as determined by search results obtained bythe predictor 435, an input picture may have prediction references drawnfrom multiple reference pictures stored in the reference picture memory434.

The controller 450 may manage coding operations of the video coder 430,including, for example, setting of parameters and subgroup parametersused for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder 445. The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter 440 may buffer the coded video sequence(s) as created bythe entropy coder 445 to prepare it for transmission via a communicationchannel 460, which may be a hardware/software link to a storage devicewhich would store the encoded video data. The transmitter 440 may mergecoded video data from the video coder 430 with other data to betransmitted, for example, coded audio data and/or ancillary data streams(sources not shown).

The controller 450 may manage operation of the encoder 203. Duringcoding, the controller 450 may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder 203 may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder 203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter 440 may transmit additional data withthe encoded video. The video coder 4 may include such data as part ofthe coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Before describing certain aspects of the disclosed subject matter inmore detail, a few terms need to be introduced that will be referred toin the remainder of this description.

Sub-Picture henceforth refers to an, in some cases, rectangulararrangement of samples, blocks, macroblocks, coding units, or similarentities that are semantically grouped, and that may be independentlycoded in changed resolution. One or more sub-pictures may for a picture.One or more coded sub-pictures may form a coded picture. One or moresub-pictures may be assembled into a picture, and one or more subpictures may be extracted from a picture. In certain environments, oneor more coded sub-pictures may be assembled in the compressed domainwithout transcoding to the sample level into a coded picture, and in thesame or certain other cases, one or more coded sub-pictures may beextracted from a coded picture in the compressed domain.

Adaptive Resolution Change (ARC) henceforth refers to mechanisms thatallow the change of resolution of a picture or sub-picture within acoded video sequence, by the means of, for example, reference pictureresampling. ARC parameters henceforth refer to the control informationrequired to perform adaptive resolution change, that may include, forexample, filter parameters, scaling factors, resolutions of outputand/or reference pictures, various control flags, and so forth.

Above description is focused on coding and decoding a single,semantically independent coded video picture. Before describing theimplication of coding/decoding of multiple sub pictures with independentARC parameters and its implied additional complexity, options forsignaling ARC parameters shall be described.

Referring to FIG. 5, shown are several novel options for signaling ARCparameters. As noted with each of the options, they have certainadvantages and certain disadvantages from a coding efficiency,complexity, and architecture viewpoint. A video coding standard ortechnology may choose one or more of these options, or options knownfrom previous art, for signaling ARC parameters. The options may not bemutually exclusive, and conceivably may be interchanged based onapplication needs, standards technology involved, or encoder's choice.

Classes of ARC parameters may include:

-   -   up/downsample factors, separate or combined in X and Y dimension    -   up/downsample factors, with an addition of a temporal dimension,        indicating constant speed zoom in/out for a given number of        pictures    -   Either of the above two may involve the coding of one or more        presumably short syntax elements that may point into a table        containing the factor(s).    -   resolution, in X or Y dimension, in units of samples, blocks,        macroblocks, CUs, or any other suitable granularity, of the        input picture, output picture, reference picture, coded picture,        combined or separately. If there are more than one resolution        (such as, for example, one for input picture, one for reference        picture) then, in certain cases, one set of values may be        inferred to from another set of values. Such could be gated, for        example, by the use of flags. For a more detailed example, see        below.    -   “warping” coordinates akin those used in H.263 Annex P, again in        a suitable granularity as described above. H.263 Annex P defines        one efficient way to code such warping coordinates, but other,        potentially more efficient ways could conceivably also be        devised. For example, the variable length reversible,        “Huffman”-style coding of warping coordinates of Annex P could        be replaced by a suitable length binary coding, where the length        of the binary code word could, for example, be derived from a        maximum picture size, possibly multiplied by a certain factor        and offset by a certain value, so to allow for “warping” outside        of the maximum picture size's boundaries.    -   up or downsample filter parameters. In the easiest case, there        may be only a single filter for up and/or downsampling. However,        in certain cases, it can be advantageous to allow more        flexibility in filter design, and that may require to signaling        of filter parameters. Such parameters may be selected through an        index in a list of possible filter designs, the filter may be        fully specified (for example through a list of filter        coefficients, using suitable entropy coding techniques), the        filter may be implicitly selected through up/downsample ratios        according which in turn are signaled according to any of the        mechanisms mentioned above, and so forth.

Henceforth, the description assumes the coding of a finite set ofup/downsample factors (the same factor to be used in both X and Ydimension), indicated through a codeword. That codeword canadvantageously be variable length coded, for example using theExt-Golomb code common for certain syntax elements in video codingspecifications such as H.264 and H.265. One suitable mapping of valuesto up/downsample factors can, for example, be according to the followingtable

Codeword Ext-Golomb Code Original/Target resolution 0 1 1/1 1 010 1/1.5(upscale by 50%) 2 011 1.5/1 (downscale by 50%) 3 00100 1/2 (upscale by100%) 4 00101 2/1 (downscale by 100%)

Many similar mappings could be devised according to the needs of anapplication and the capabilities of the up and downscale mechanismsavailable in a video compression technology or standard. The table couldbe extended to more values. Values may also be represented by entropycoding mechanisms other than Ext-Golomb codes, for example using binarycoding. That may have certain advantages when the resampling factorswere of interest outside the video processing engines (encoder anddecoder foremost) themselves, for example by MANES. It should be notedthat, for the (presumably) most common case where no resolution changeis required, an Ext-Golomb code can be chosen that is short; in thetable above, only a single bit. That can have a coding efficiencyadvantage over using binary codes for the most common case.

The number of entries in the table, as well as their semantics may befully or partially configurable. For example, the basic outline of thetable may be conveyed in a “high” parameter set such as a sequence ordecoder parameter set. Alternatively or in addition, one or more suchtables may be defined in a video coding technology or standard, and maybe selected through for example a decoder or sequence parameter set.

Henceforth, we describe how an upsample/downsample factor (ARCinformation), coded as described above, may be included in a videocoding technology or standard syntax. Similar considerations may applyto one, or a few, codewords controlling up/downsample filters. See belowfor a discussion when comparatively large amounts of data are requiredfor a filter or other data structures.

H.263 Annex P shown in illustration 500A includes the ARC information502 in the form of four warping coordinates into the picture header 501,specifically in the H.263 PLUSPTYPE 503 header extension. This can be asensible design choice when a) there is a picture header available, andb) frequent changes of the ARC information are expected. However, theoverhead when using H.263-style signaling can be quite high, and scalingfactors may not pertain among picture boundaries as picture header canbe of transient nature.

JVCET-M135-v1, cited above, includes the ARC reference information 505(an index) located in a picture parameter set 504, indexing a table 506including target resolutions that in turn is located inside a sequenceparameter set 507. The placement of the possible resolution in a table506 in the sequence parameter set 507 can, according to verbalstatements made by the authors, be justified by using the SPS as aninteroperability negotiation point during capability exchange.Resolution can change, within the limits set by the values in the table506 from picture to picture by referencing the appropriate pictureparameter set 504.

Still referring to FIG. 5, the following additional options may exist toconvey ARC information in a video bitstream. Each of those options hascertain advantages over existing art as described above. The options maybe simultaneously present in the same video coding technology orstandard.

In an embodiment, ARC information 509, as in illustration 500B, such asa resampling (zoom) factor may be present in a slice header, GOB header,tile header, or tile group header (tile group header henceforth) 508.This can be adequate of the ARC information is small, such as a singlevariable length ue(v) or fixed length codeword of a few bits, forexample as shown above. Having the ARC information in a tile groupheader directly has the additional advantage of the ARC information maybe applicable to a sub picture represented by, for example, that tilegroup, rather than the whole picture. See also below. In addition, evenif the video compression technology or standard envisions only wholepicture adaptive resolution changes (in contrast to, for example, tilegroup based adaptive resolution changes), putting the ARC informationinto the tile group header vis a vis putting it into an H.263-stylepicture header has certain advantages from an error resilienceviewpoint.

In the same or another embodiment, the ARC information 512 itself may bepresent in an appropriate parameter set 511 such as, for example, apicture parameter set, header parameter set, tile parameter set,adapation parameter set, and so forth (Adapation parameter setdepicted). The scope of that parameter set can advantageously be nolarger than a picture, for example a tile group. The use of the ARCinformation is implicit through the activation of the relevant parameterset. For example, when a video coding technology or standardcontemplates only picture-based ARC, then a picture parameter set orequivalent may be appropriate.

in the same or another embodiment, ARC reference information 513 may bepresent in a Tile Group header 514 or a similar data structure. Thatreference information 513 can refer to a subset of ARC information 515available in a parameter set 516 with a scope beyond a single picture,for example a sequence parameter set, or decoder parameter set.

The additional level of indirection implied activation of a PPS from atile group header, PPS, SPS, as used in WET-M0135-v1 appears to beunnecessary, as picture parameter sets, just as sequence parameter sets,can (and have in certain standards such as RFC3984) be used forcapability negotiation or announcements. If, however, the ARCinformation should be applicable to a sub picture represented, forexample, by a tile groups also, a parameter set with an activation scopelimited to a tile group, such as the Adaptation Parameter set or aHeader Parameter Set may be the better choice. Also, if the ARCinformation is of more than negligible size—for example contains filtercontrol information such as numerous filter coefficients—then aparameter may be a better choice than using a header 508 directly from acoding efficiency viewpoint, as those settings may be reusable by futurepictures or sub-pictures by referencing the same parameter set.

When using the sequence parameter set or another higher parameter setwith a scope spanning multiple pictures, certain considerations mayapply:

1. The parameter set to store the ARC information table 516 can, in somecases, be the sequence parameter set, but in other cases advantageouslythe decoder parameter set. The decoder parameter set can have anactivation scope of multiple CVSs, namely the coded video stream, i.e.all coded video bits from session start until session teardown. Such ascope may be more appropriate because possible ARC factors may be adecoder feature, possibly implemented in hardware, and hardware featurestend not to change with any CVS (which in at least some entertainmentsystems is a Group of Pictures, one second or less in length). Thatsaid, putting the table into the sequence parameter set is expresslyincluded in the placement options described herein, in particular inconjunction with point 2 below.

2. The ARC reference information 513 may advantageously be placeddirectly into the picture/slice tile/GOB/tile group header (tile groupheader henceforth) 514 rather than into the picture parameter set as inJVCET-M0135-v1, The reason is as follows: when an encoder wants tochange a single value in a picture parameter set, such as for examplethe ARC reference information, then it has to create a new PPS andreference that new PPS. Assume that only the ARC reference informationchanges, but other information such as, for example, the quantizationmatrix information in the PPS stays. Such information can be ofsubstantial size, and would need to be retransmitted to make the new PPScomplete. As the ARC reference information may be a single codeword,such as the index into the table 513 and that would be the only valuethat changes, it would be cumbersome and wasteful to retransmit all the,for example, quantization matrix information. Insofar, can beconsiderably better from a coding efficiency viewpoint to avoid theindirection through the PPS, as proposed in WET-M0135-v1. Similarly,putting the ARC reference information into the PPS has the additionaldisadvantage that the ARC information referenced by the ARC referenceinformation 513 necessarily needs to apply to the whole picture and notto a sub-picture, as the scope of a picture parameter set activation isa picture.

In the same or another embodiment, the signaling of ARC parameters canfollow a detailed example as outlined in FIG. 6. FIG. 6 depicts syntaxdiagrams 600 in a representation as used in video coding standards sinceat least 1993. The notation of such syntax diagrams roughly followsC-style programming. Lines in boldface indicate syntax elements presentin the bitstream, lines without boldface often indicate control flow orthe setting of variables.

A tile group header 601 as an exemplary syntax structure of a headerapplicable to a (possibly rectangular) part of a picture canconditionally contain, a variable length, Exp-Golomb coded syntaxelement dec_pic_size_idx 602 (depicted in boldface). The presence ofthis syntax element in the tile group header can be gated on the use ofadaptive resolution 603—here, the value of a flag not depicted inboldface, which means that flag is present in the bitstream at the pointwhere it occurs in the syntax diagram. Whether or not adaptiveresolution is in use for this picture or parts thereof can be signaledin any high level syntax structure inside or outside the bitstream. Inthe example shown, it is signaled in the sequence parameter set asoutlined below.

Still referring to FIG. 6, shown is also an excerpt of a sequenceparameter set 610. The first syntax element shown isadaptive_pic_resolution_change_flag 611. When true, that flag canindicate the use of adaptive resolution which, in turn may requirecertain control information. In the example, such control information isconditionally present based on the value of the flag based on the if( )statement in the parameter set 612 and the tile group header 601.

When adaptive resolution is in use, in this example, coded is an outputresolution in units of samples 613. The numeral 613 refers to bothoutput_pic_width_in_luma_samples and output_pic_height_in_luma_samples,which together can define the resolution of the output picture.Elsewhere in a video coding technology or standard, certain restrictionsto either value can be defined. For example, a level definition maylimit the number of total output samples, which could be the product ofthe value of those two syntax elements. Also, certain video codingtechnologies or standards, or external technologies or standards suchas, for example, system standards, may limit the numbering range (forexample, one or both dimensions must be divisible by a power of 2number), or the aspect ratio (for example, the width and height must bein a relation such as 4:3 or 16:9). Such restrictions may be introducedto facilitate hardware implementations or for other reasons, and arewell known in the art.

In certain applications, it can be advisable that the encoder instructsthe decoder to use a certain reference picture size rather thanimplicitly assume that size to be the output picture size. In thisexample, the syntax element reference_pic_size_present_flag 614 gatesthe conditional presence of reference picture dimensions 615 (again, thenumeral refers to both width and height).

Finally, shown is a table of possible decoding picture width andheights. Such a table can be expressed, for example, by a tableindication (num_dec_pic_size_in_luma_samples_minus1) 616. The “minus1”can refer to the interpretation of the value of that syntax element. Forexample, if the coded value is zero, one table entry is present. If thevalue is five, six table entries are present. For each “line” in thetable, decoded picture width and height are then included in the syntax617.

The table entries presented 617 can be indexed using the syntax elementdec_pic_size_idx 602 in the tile group header, thereby allowingdifferent decoded sizes—in effect, zoom factors—per tile group.

Certain video coding technologies or standards, for example VP9, supportspatial scalability by implementing certain forms of reference pictureresampling (signaled quite differently from the disclosed subjectmatter) in conjunction with temporal scalability, so to enable spatialscalability. In particular, certain reference pictures may be upsampledusing ARC-style technologies to a higher resolution to form the base ofa spatial enhancement layer. Those upsampled pictures could be refined,using normal prediction mechanisms at the high resolution, so to adddetail.

The disclosed subject matter can be used in such an environment. Incertain cases, in the same or another embodiment, a value in the NALunit header, for example the Temporal ID field, can be used to indicatenot only the temporal but also the spatial layer. Doing so has certainadvantages for certain system designs; for example, existing SelectedForwarding Units (SFU) created and optimized for temporal layer selectedforwarding based on the NAL unit header Temporal ID value can be usedwithout modification, for scalable environments. In order to enablethat, there may be a requirement for a mapping between the coded picturesize and the temporal layer is indicated by the temporal ID field in theNAL unit header.

In some video coding technologies, an Access Unit (AU) can refer tocoded picture(s), slice(s), tile(s), NAL Unit(s), and so forth, thatwere captured and composed into a the respective picture/slice/tile/NALunit bitstream at a given instance in time. That instance in time can bethe composition time.

In HEVC, and certain other video coding technologies, a picture ordercount (POC) value can be used for indicating a selected referencepicture among multiple reference picture stored in a decoded picturebuffer (DPB). When an access unit (AU) comprises one or more pictures,slices, or tiles, each picture, slice, or tile belonging to the same AUmay carry the same POC value, from which it can be derived that theywere created from content of the same composition time. In other words,in a scenario where two pictures/slices/tiles carry the same given POCvalue, that can be indicative of the two picture/slice/tile belonging tothe same AU and having the same composition time. Conversely, twopictures/tiles/slices having different POC values can indicate thosepictures/slices/tiles belonging to different AUs and having differentcomposition times.

In an embodiment of the disclosed subject matter, aforementioned rigidrelationship can be relaxed in that an access unit can comprisepictures, slices, or tiles with different POC values. By allowingdifferent POC values within an AU, it becomes possible to use the POCvalue to identify potentially independently decodablepictures/slices/tiles with identical presentation time. That, in turn,can enable support of multiple scalable layers without a change ofreference picture selection signaling (e.g. reference picture setsignaling or reference picture list signaling), as described in moredetail below.

It is, however, still desirable to be able to identify the AU that apicture/slice/tile belongs to, with respect to otherpicture/slices/tiles having different POC values, from the POC valuealone. This can be achieved, as described below.

In the same or other embodiments, an access unit count (AUC) may besignaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The value of AUC may be used to identify which NAL units,pictures, slices, or tiles belong to a given AU. The value of AUC may becorresponding to a distinct composition time instance. The AUC value maybe equal to a multiple of the POC value. By dividing the POC value by aninteger value, the AUC value may be calculated. In certain cases,division operations can place a certain burden on decoderimplementations. In such cases, small restrictions in the numberingspace of the AUC values may allow to substitute the division operationby shift operations. For example, the AUC value may be equal to a MostSignificant Bit (MSB) value of the POC value range.

In the same embodiment, a value of POC cycle per AU (poc_cycle_au) maybe signaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The poc_cycle_au may indicate how many different andconsecutive POC values can be associated with the same AU. For example,if the value of poc_cycle_au is equal to 4, the pictures, slices ortiles with the POC value equal to 0-3, inclusive, are associated withthe AU with AUC value equal to 0, and the pictures, slices or tiles withPOC value equal to 4-7, inclusive, are associated with the AU with AUCvalue equal to 1. Hence, the value of AUC may be inferred by dividingthe POC value by the value of poc_cycle_au.

In the same or another embodiment, the value of poc_cycle_au may bederived from information, located for example in the video parameter set(VPS), that identifies the number of spatial or SNR layers in a codedvideo sequence. Such a possible relationship is briefly described below.While the derivation as described above may save a few bits in the VPSand hence may improves coding efficiency, it can be advantageous toexplicitly code poc_cycle_au in an appropriate high level syntaxstructure hierarchically below the video parameter set, so to be able tominimize poc_cycle_au for a given small part of a bitstream such as apicture. This optimization may save more bits than can be saved throughthe derivation process above because POC values (and/or values of syntaxelements indirectly referring to POC) may be coded in low level syntaxstructures.

In the same or another embodiment, FIG. 9 shows an example of syntaxtables 900 to signal the syntax element of vps_poc_cycle_au in VPS (orSPS), which indicates the poc_cycle_au used for all picture/slices in acoded video sequence, and the syntax element of slice_poc_cycle_au,which indicates the poc_cycle_au of the current slice, in slice header.If the POC value increases uniformly per AU,vps_contant_poc_cycle_per_au in VPS is set equal to 1 andvps_poc_cycle_au is signaled in VPS. In this case, slice_poc_cycle_au isnot explicitly signaled, and the value of AUC for each AU is calculatedby dividing the value of POC by vps_poc_cycle_au. If the POC value doesnot increase uniformly per AU, vps_contant_poc_cycle_per_au in VPS isset equal to 0. In this case, vps_access_unit_cnt is not signaled, whileslice_access_unit_cnt is signaled in slice header for each slice orpicture. Each slice or picture may have a different value ofslice_access_unit_cnt. The value of AUC for each AU is calculated bydividing the value of POC by slice_poc_cycle_au. FIG. 10 shows a blockdiagram illustrating the relevant work flow 1000.

At S10, there is considered parsing VPS/SPS, and identifying whether oneor more POC cycle per AU is constant. At S11, it is determined whetherthe POC cycle per AU is constant within a coded video sequence, and ifnot, at S13, there is calculating of the value of access unit count froma picture level poc_cycle_au_value and a POC value, and if so, at S12there is calculating of the value of access unit count from a sequencelevel poc_cycle_au_value and a POC value. At S14, there is parsingVPS/SPS and identifying of whether the POC cycle per AU is constant ornot which may begin again such steps described above or proceed on toalternate processing.

In the same or other embodiments, even though the value of POC of apicture, slice, or tile may be different, the picture, slice, or tilecorresponding to an AU with the same AUC value may be associated withthe same decoding or output time instance. Hence, without anyinter-parsing/decoding dependency across pictures, slices or tiles inthe same AU, all or subset of pictures, slices or tiles associated withthe same AU may be decoded in parallel, and may be outputted at the sametime instance.

In the same or other embodiments, even though the value of POC of apicture, slice, or tile may be different, the picture, slice, or tilecorresponding to an AU with the same AUC value may be associated withthe same composition/display time instance. When the composition time iscontained in a container format, even though pictures correspond todifferent AUs, if the pictures have the same composition time, thepictures can be displayed at the same time instance.

In the same or other embodiments, each picture, slice, or tile may havethe same temporal identifier (temporal_id) in the same AU. All or subsetof pictures, slices or tiles corresponding to a time instance may beassociated with the same temporal sub-layer. In the same or otherembodiments, each picture, slice, or tile may have the same or adifferent spatial layer id (layer_id) in the same AU. All or subset ofpictures, slices or tiles corresponding to a time instance may beassociated with the same or a different spatial layer.

FIG. 8 shows an example of a video sequence structure with combinationof temporal_id, layer_id, POC and AUC values with adaptive resolutionchange. In this example, a picture, slice or tile in the first AU withAUC=0 may have temporal_id=0 and layer_id=0 or 1, while a picture, sliceor tile in the second AU with AUC=1 may have temporal_id=1 andlayer_id=0 or 1, respectively. The value of POC is increased by 1 perpicture regardless of the values of temporal_id and layer_id. In thisexample, the value of poc_cycle_au can be equal to 2. Preferably, thevalue of poc_cycle_au may be set equal to the number of (spatialscalability) layers. In this example, hence, the value of POC isincreased by 2, while the value of AUC is increased by 1.

In the above embodiments, all or sub-set of inter-picture or inter-layerprediction structure and reference picture indication may be supportedby using the existing reference picture set (RPS) signaling in HEVC orthe reference picture list (RPL) signaling. In RPS or RPL, the selectedreference picture is indicated by signaling the value of POC or thedelta value of POC between the current picture and the selectedreference picture. For the disclosed subject matter, the RPS and RPL canbe used to indicate the inter-picture or inter-layer predictionstructure without change of signaling, but with the followingrestrictions. If the value of temporal_id of a reference picture isgreater than the value of temporal_id current picture, the currentpicture may not use the reference picture for motion compensation orother predictions. If the value of layer_id of a reference picture isgreater than the value of layer_id current picture, the current picturemay not use the reference picture for motion compensation or otherpredictions.

In the same and other embodiments, the motion vector scaling based onPOC difference for temporal motion vector prediction may be disabledacross multiple pictures within an access unit. Hence, although eachpicture may have a different POC value within an access unit, the motionvector is not scaled and used for temporal motion vector predictionwithin an access unit. This is because a reference picture with adifferent POC in the same AU is considered a reference picture havingthe same time instance. Therefore, in the embodiment, the motion vectorscaling function may return 1, when the reference picture belongs to theAU associated with the current picture.

In the same and other embodiments, the motion vector scaling based onPOC difference for temporal motion vector prediction may be optionallydisabled across multiple pictures, when the spatial resolution of thereference picture is different from the spatial resolution of thecurrent picture. When the motion vector scaling is allowed, the motionvector is scaled based on both POC difference and the spatial resolutionratio between the current picture and the reference picture.

In the same or another embodiment, the motion vector may be scaled basedon AUC difference instead of POC difference, for temporal motion vectorprediction, especially when the poc_cycle_au has non-uniform value (whenvps_contant_poc_cycle_per_au==0). Otherwise (whenvps_contant_poc_cycle_per_au==1), the motion vector scaling based on AUCdifference may be identical to the motion vector scaling based on POCdifference.

In the same or another embodiment, when the motion vector is scaledbased on AUC difference, the reference motion vector in the same AU(with the same AUC value) with the current picture is not scaled basedon AUC difference and used for motion vector prediction without scalingor with scaling based on spatial resolution ratio between the currentpicture and the reference picture.

In the same and other embodiments, the AUC value is used for identifyingthe boundary of AU and used for hypothetical reference decoder (HRD)operation, which needs input and output timing with AU granularity. Inmost cases, the decoded picture with the highest layer in an AU may beoutputted for display. The AUC value and the layer_id value can be usedfor identifying the output picture.

In an embodiment, a picture may consist of one or more sub-pictures.Each sub-picture may cover a local region or the entire region of thepicture. The region supported by a sub-picture may or may not beoverlapped with the region supported by another sub-picture. The regioncomposed by one or more sub-pictures may or may not cover the entireregion of a picture. If a picture consists of a sub-picture, the regionsupported by the sub-picture is identical to the region supported by thepicture.

In the same embodiment, a sub-picture may be coded by a coding methodsimilar to the coding method used for the coded picture. A sub-picturemay be independently coded or may be coded dependent on anothersub-picture or a coded picture. A sub-picture may or may not have anyparsing dependency from another sub-picture or a coded picture.

In the same embodiment, a coded sub-picture may be contained in one ormore layers. A coded sub-picture in a layer may have a different spatialresolution. The original sub-picture may be spatially re-sampled(up-sampled or down-sampled), coded with different spatial resolutionparameters, and contained in a bitstream corresponding to a layer.

In the same or another embodiment, a sub-picture with (W, II), where Windicates the width of the sub-picture and H indicates the height of thesub-picture, respectively, may be coded and contained in the codedbitstream corresponding to layer 0, while the up-sampled (ordown-sampled) sub-picture from the sub-picture with the original spatialresolution, with (W*S_(w,k), H*S_(h,k)), may be coded and contained inthe coded bitstream corresponding to layer k, where S_(w,k), S_(h,k)indicate the resampling ratios, horizontally and vertically. If thevalues of S_(w,k), S_(h,k) are greater than 1, the resampling is equalto the up-sampling. Whereas, if the values of S_(w,k), S_(h,k) aresmaller than 1, the resampling is equal to the down-sampling.

In the same or another embodiment, a coded sub-picture in a layer mayhave a different visual quality from that of the coded sub-picture inanother layer in the same sub-picture or different subpicture. Forexample, sub-picture i in a layer, n, is coded with the quantizationparameter, Q_(i,n), while a sub-picture j in a layer, m, is coded withthe quantization parameter, Q_(j,m).

In the same or another embodiment, a coded sub-picture in a layer may beindependently decodable, without any parsing or decoding dependency froma coded sub-picture in another layer of the same local region. Thesub-picture layer, which can be independently decodable withoutreferencing another sub-picture layer of the same local region, is theindependent sub-picture layer. A coded sub-picture in the independentsub-picture layer may or may not have a decoding or parsing dependencyfrom a previously coded sub-picture in the same sub-picture layer, butthe coded sub-picture may not have any dependency from a coded picturein another sub-picture layer.

In the same or another embodiment, a coded sub-picture in a layer may bedependently decodable, with any parsing or decoding dependency from acoded sub-picture in another layer of the same local region. Thesub-picture layer, which can be dependently decodable with referencinganother sub-picture layer of the same local region, is the dependentsub-picture layer. A coded sub-picture in the dependent sub-picture mayreference a coded sub-picture belonging to the same sub-picture, apreviously coded sub-picture in the same sub-picture layer, or bothreference sub-pictures.

In the same or another embodiment, a coded sub-picture consists of oneor more independent sub-picture layers and one or more dependentsub-picture layers. However, at least one independent sub-picture layermay be present for a coded sub-picture. The independent sub-picturelayer may have the value of the layer identifier (layer_id), which maybe present in NAL unit header or another high-level syntax structure,equal to 0. The sub-picture layer with the layer_id equal to 0 is thebase sub-picture layer.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures and one background sub-picture. The regionsupported by a background sub-picture may be equal to the region of thepicture. The region supported by a foreground sub-picture may beoverlapped with the region supported by a background sub-picture. Thebackground sub-picture may be a base sub-picture layer, while theforeground sub-picture may be a non-base (enhancement) sub-picturelayer. One or more non-base sub-picture layer may reference the samebase layer for decoding. Each non-base sub-picture layer with layer_idequal to a may reference a non-base sub-picture layer with layer_idequal to b, where a is greater than b.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Eachsub-picture may have its own base sub-picture layer and one or morenon-base (enhancement) layers. Each base sub-picture layer may bereferenced by one or more non-base sub-picture layers. Each non-basesub-picture layer with layer_id equal to a may reference a non-basesub-picture layer with layer_id equal to b, where a is greater than b.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Eachcoded sub-picture in a (base or non-base) sub-picture layer may bereferenced by one or more non-base layer sub-pictures belonging to thesame sub-picture and one or more non-base layer sub-pictures, which arenot belonging to the same sub-picture.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Asub-picture in a layer a may be further partitioned into multiplesub-pictures in the same layer. One or more coded sub-pictures in alayer b may reference the partitioned sub-picture in a layer a.

In the same or another embodiment, a coded video sequence (CVS) may be agroup of the coded pictures. The CVS may consist of one or more codedsub-picture sequences (CSPS), where the CSPS may be a group of codedsub-pictures covering the same local region of the picture. A CSPS mayhave the same or a different temporal resolution than that of the codedvideo sequence.

In the same or another embodiment, a CSPS may be coded and contained inone or more layers. A CSPS may consist of one or more CSPS layers.Decoding one or more CSPS layers corresponding to a CSPS may reconstructa sequence of sub-pictures corresponding to the same local region.

In the same or another embodiment, the number of CSPS layerscorresponding to a CSPS may be identical to or different from the numberof CSPS layers corresponding to another CSPS.

In the same or another embodiment, a CSPS layer may have a differenttemporal resolution (e.g. frame rate) from another CSPS layer. Theoriginal (uncompressed) sub-picture sequence may be temporallyre-sampled (up-sampled or down-sampled), coded with different temporalresolution parameters, and contained in a bitstream corresponding to alayer.

In the same or another embodiment, a sub-picture sequence with the framerate, F, may be coded and contained in the coded bitstream correspondingto layer 0, while the temporally up-sampled (or down-sampled)sub-picture sequence from the original sub-picture sequence, withF*S_(t,k), may be coded and contained in the coded bitstreamcorresponding to layer k, where S_(t,k) indicates the temporal samplingratio for layer k. If the value of S_(t,k) is greater than 1, thetemporal resampling process is equal to the frame rate up conversion.Whereas, if the value of S_(t,k) is smaller than 1, the temporalresampling process is equal to the frame rate down conversion.

In the same or another embodiment, when a sub-picture with a CSPS layera is reference by a sub-picture with a CSPS layer b for motioncompensation or any inter-layer prediction, if the spatial resolution ofthe CSPS layer a is different from the spatial resolution of the CSPSlayer b, decoded pixels in the CSPS layer a are resampled and used forreference. The resampling process may need an up-sampling filtering or adown-sampling filtering.

FIG. 11 shows an example 1100 with respect to a video bitstreamincluding a background video CSPS with layer_id equal to 0 and multipleforeground CSPS layers. While a coded sub-picture may consist of one ormore CSPS layers, a background region, which does not belong to anyforeground CSPS layer, may consist of a base layer. The base layer maycontain a background region and foreground regions, while an enhancementCSPS layer contain a foreground region. An enhancement CSPS layer mayhave a better visual quality than the base layer, at the same region.The enhancement CSPS layer may reference the reconstructed pixels andthe motion vectors of the base layer, corresponding to the same region.

In the same or another embodiment, the video bitstream corresponding toa base layer is contained in a track, while the CSPS layerscorresponding to each sub-picture are contained in a separated track, ina video file.

In the same or another embodiment, the video bitstream corresponding toa base layer is contained in a track, while CSPS layers with the samelayer_id are contained in a separated track. In this example, a trackcorresponding to a layer k includes CSPS layers corresponding to thelayer k, only.

In the same or another embodiment, each CSPS layer of each sub-pictureis stored in a separate track. Each trach may or may not have anyparsing or decoding dependency from one or more other tracks.

In the same or another embodiment, each track may contain bitstreamscorresponding to layer i to layer j of CSPS layers of all or a subset ofsub-pictures, where 0<i=<j=<k, k being the highest layer of CSPS.

In the same or another embodiment, a picture consists of one or moreassociated media data including depth map, alpha map, 3D geometry data,occupancy map, etc. Such associated timed media data can be divided toone or multiple data sub-stream each of which corresponding to onesub-picture.

In the same or another embodiment, FIG. 12 shows an example 1200 ofvideo conference based on the multi-layered sub-picture method. In avideo stream, one base layer video bitstream 1201 corresponding to thebackground picture and one or more enhancement layer video bitstreams1202 corresponding to foreground sub-pictures are contained. Eachenhancement layer video bitstream 1202 is corresponding to a CSPS layer.In a display, the picture corresponding to the base layer is displayedby default. It contains one or more user's picture in a picture (PIP).When a specific user is selected by a client's control, the enhancementCSPS layer 1202 corresponding to the selected user is decoded anddisplayed with the enhanced quality or spatial resolution. FIG. 13 showsthe diagram 1300 for the operation.

At S20, there is a decoding of video bitstream with multi-layers, and atS21 there is an identifying of a background region and one or moreforeground sub-pictures. At S22, there is considered whether a specificsub-picture region is selected, and if not, at S24, there is decoded anddisplayed the background region, and if so, at S23, there is decoded anddisplayed the enhanced sub-picture.

In the same or another embodiment, a network middle box (such as router)may select a subset of layers to send to a user depending on itsbandwidth. The picture/subpicture organization may be used for bandwidthadaptation. For instance, if the user doesn't have the bandwidth, therouter strips of layers or selects some subpictures due to theirimportance or based on used setup and this can be done dynamically toadopt to bandwidth.

FIG. 14 shows a use case of 360 video 1400. When a spherical 360 picture1401 is projected onto a planar picture, the projection 360 picture maybe partitioned into multiple sub-pictures as a base layer 1402. Anenhancement layer 1403 of a specific sub-picture may be coded andtransmitted to a client. A decoder may be able to decode both the baselayer including all sub-pictures and an enhancement layer of a selectedsub-picture. When the current viewport is identical to the selectedsub-picture, the displayed picture may have a higher quality with thedecoded sub-picture with the enhancement layer. Otherwise, the decodedpicture with the base layer can be displayed, with a low quality.

In the same or another embodiment, any layout information for displaymay be present in a file, as supplementary information (such as SEImessage or metadata). One or more decoded sub-pictures may be relocatedand displayed depending on the signaled layout information. The layoutinformation may be signaled by a streaming server or a broadcaster, ormay be regenerated by a network entity or a cloud server, or may bedetermined by a user's customized setting.

In an embodiment, when an input picture is divided into one or more(rectangular) sub-region(s), each sub-region may be coded as anindependent layer. Each independent layer corresponding to a localregion may have a unique layer_id value. For each independent layer, thesub-picture size and location information may be signaled. For example,picture size (width, height), the offset information of the left-topcorner (x_offset, y_offset). FIG. 15 shows an example 1500 of the layoutof divided sub-pictures, its sub-picture size and position informationand its corresponding picture prediction structure. The layoutinformation including the sub-picture size(s) and the sub-pictureposition(s) may be signaled in a high-level syntax structure, such asparameter set(s), header of slice or tile group, or SEI message.

In the same embodiment, each sub-picture corresponding to an independentlayer may have its unique POC value within an AU. When a referencepicture among pictures stored in DPB is indicated by using syntaxelement(s) in RPS or RPL structure, the POC value(s) of each sub-picturecorresponding to a layer may be used.

In the same or another embodiment, in order to indicate the(inter-layer) prediction structure, the layer_id may not be used and thePOC (delta) value may be used.

In the same embodiment, a sub-picture with a POC vale equal to Ncorresponding to a layer (or a local region) may or may not be used as areference picture of a sub-picture with a POC value equal to N+K,corresponding to the same layer (or the same local region) for motioncompensated prediction. In most cases, the value of the number K may beequal to the maximum number of (independent) layers, which may beidentical to the number of sub-regions.

In the same or another embodiment, FIG. 16 shows the extended case ofFIG. 15. When an input picture is divided into multiple (e.g. four)sub-regions, each local region may be coded with one or more layers. Inthe case, the number of independent layers may be equal to the number ofsub-regions, and one or more layers may correspond to a sub-region.Thus, each sub-region may be coded with one or more independent layer(s)and zero or more dependent layer(s).

In the same embodiment, in FIG. 16, an example illustration 1600 isshown in which the input picture may be divided into four sub-regions.The right-top sub-region may be coded as two layers, which are layer 1and layer 4, while the right-bottom sub-region may be coded as twolayers, which are layer 3 and layer 5. In this case, the layer 4 mayreference the layer 1 for motion compensated prediction, while the layer5 may reference the layer 3 for motion compensation.

In the same or another embodiment, in-loop filtering (such as deblockingfiltering, adaptive in-loop filtering, reshaper, bilateral filtering orany deep-learning based filtering) across layer boundary may be(optionally) disabled.

In the same or another embodiment, motion compensated prediction orintra-block copy across layer boundary may be (optionally) disabled.

In the same or another embodiment, boundary padding for motioncompensated prediction or in-loop filtering at the boundary ofsub-picture may be processed optionally. A flag indicating whether theboundary padding is processed or not may be signaled in a high-levelsyntax structure, such as parameter set(s) (VPS, SPS, PPS, or APS),slice or tile group header, or SEI message.

In the same or another embodiment, the layout information ofsub-region(s) (or sub-picture(s)) may be signaled in VPS or SPS. FIG. 17shows an example 1700 of the syntax elements in VPS and SPS. In thisexample, vps_sub_picture_dividing_flag is signalled in VPS. The flag mayindicate whether input picture(s) are divided into multiple sub-regionsor not. When the value of vps_sub_picture_dividing_flag is equal to 0,the input picture(s) in the coded video sequence(s) corresponding to thecurrent VPS may not be divided into multiple sub-regions. In this case,the input picture size may be equal to the coded picture size(pic_width_in_luma_samples, pic_height_in_luma_samples), which issignaled in SPS. When the value of vps_sub_picture_dividing_flag isequal to 1, the input picture(s) may be divided into multiplesub-regions. In this case, the syntax elementsvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples are signaled in VPS. The values ofvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may be equal to the width and heightof the input picture(s), respectively.

In the same embodiment, the values of vps_full_pic_width_in_luma_samplesand vps_full_pic_height_in_luma_samples may not be used for decoding,but may be used for composition and display.

In the same embodiment, when the value of vps_sub_picture_dividing_flagis equal to 1, the syntax elements pic_offset_x and pic_offset_y may besignaled in SPS, which corresponds to (a) specific layer(s). In thiscase, the coded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples) signaled in SPS may be equal to the widthand height of the sub-region corresponding to a specific layer. Also,the position (pic_offset_x, pic_offset_y) of the left-top corner of thesub-region may be signaled in SPS.

In the same embodiment, the position information (pic_offset_x,pic_offset_y) of the left-top corner of the sub-region may not be usedfor decoding, but may be used for composition and display.

In the same or another embodiment, the layout information (size andposition) of all or sub-set sub-region(s) of (an) input picture(s), thedependency information between layer(s) may be signaled in a parameterset or an SEI message. FIG. 18 shows an example 1800 of syntax elementsto indicate the information of the layout of sub-regions, the dependencybetween layers, and the relation between a sub-region and one or morelayers. In this example, the syntax element num_sub_region indicates thenumber of (rectangular) sub-regions in the current coded video sequence.the syntax element num_layers indicates the number of layers in thecurrent coded video sequence. The value of num_layers may be equal to orgreater than the value of num_sub_region. When any sub-region is codedas a single layer, the value of num_layers may be equal to the value ofnum_sub_region. When one or more sub-regions are coded as multiplelayers, the value of num_layers may be greater than the value ofnum_sub_region. The syntax element direct_dependency_flag[i][j]indicates the dependency from the j-th layer to the i-th layer.num_layers_for_region[i] indicates the number of layers associated withthe i-th sub-region. sub_region_layer_id[i][j] indicates the layer_id ofthe j-th layer associated with the i-th sub-region. Thesub_region_offset_x[i] and sub_region_offset_y[i] indicate thehorizontal and vertical location of the left-top corner of the i-thsub-region, respectively. The sub_region_width [i] andsub_region_height[i] indicate the width and height of the i-thsub-region, respectively.

In one embodiment, one or more syntax elements that specify the outputlayer set to indicate one of more layers to be outputted with or withoutprofile tier level information may be signaled in a high-level syntaxstructure, e.g. VPS, DPS, SPS, PPS, APS or SEI message. Referring toFIG. 19, the syntax element num_output_layer_sets indicating the numberof output layer set (OLS) in the coded video sequence referring to theVPS may be signaled in the VPS. For each output layer set,output_layer_flag may be signaled as many as the number of outputlayers.

In the same embodiment, output_layer_flag[i] equal to 1 specifies thatthe i-th layer is output. vps_output_layer_flag[i] equal to 0 specifiesthat the i-th layer is not output.

In the same or another embodiment, one or more syntax elements thatspecify the profile tier level information for each output layer set maybe signaled in a high-level syntax structure, e.g. VPS, DPS, SPS, PPS,APS or SEI message. Still referring to FIG. 19, the syntax elementnum_profile_tile_level indicating the number of profile tier levelinformation per OLS in the coded video sequence referring to the VPS maybe signaled in the VPS. For each output layer set, a set of syntaxelements for profile tier level information or an index indicating aspecific profile tier level information among entries in the profiletier level information may be signaled as many as the number of outputlayers.

In the same embodiment, profile_tier_level_idx[i][j] specifies theindex, into the list of profile_tier_level( ) syntax structures in theVPS, of the profile_tier_level( ) syntax structure that applies to thej-th layer of the i-th OLS.

In the same or another embodiment, referring to the illustration 2000 ofFIG. 20, the syntax elements num_profile_tile_level and/ornum_output_layer_sets may be signaled when the number of maximum layersis greater than 1 (vps_max_layers_minus1>0).

In the same or another embodiment, referring to FIG. 20, the syntaxelement vps_output_layers_mode[i] indicating the mode of output layersignaling for the i-th output layer set may be present in VPS.

In the same embodiment, vps_output_layers_mode[i] equal to 0 specifiesthat only the highest layer is output with the i-th output layer set.vps_output_layer_mode[i] equal to 1 specifies that all layers are outputwith the i-th output layer set. vps_output_layer_mode[i] equal to 2specifies that the layers that are output are the layers withvps_output_layer_flag[i][j] equal to 1 with the i-th output layer set.More values may be reserved.

In the same embodiment, the output_layer_flag[i][j] may or may not besignaled depending on the value of vps_output_layers_mode[i] for thei-th output layer set.

In the same or another embodiment, referring to FIG. 20, the flagvps_ptl_signal_flag[i] may be present for the i-th output layer set.Depending the value of vps_ptl_signal_flag[i], the profile tier levelinformation for the i-th output layer set may or may not be signaled.

In the same or another embodiment, referring to the illustration 2100 ofFIG. 21, the number of subpicture, max_subpics_minus1, in the currentCVS may be signalled in a high-level syntax structure, e.g. VPS, DPS,SPS, PPS, APS or SEI message.

In the same embodiment, referring to FIG. 21, the subpicture identifier,sub_pic_id[i], for the i-th subpicture may be signalled, when the numberof subpictures is greater than 1 (max_subpics_minus1>0).

In the same or another embodiment, one or more syntax elementsindicating the subpicture identifier belonging to each layer of eachoutput layer set may be signalled in VPS. Referring to the illustration2200 of FIG. 22, the sub_pic_id_layer[i][j][k], which indicates the k-thsubpicture present in the j-th layer of the i-th output layer set. Withthose information, a decoder may recognize which sub-picture may bedecoded and outputted for each layer of a specific output layer set.

In an embodiment, picture header (PH) is a syntax structure containingsyntax elements that apply to all slices of a coded picture. A pictureunit (PU) is a set of NAL units that are associated with each otheraccording to a specified classification rule, are consecutive indecoding order, and contain exactly one coded picture. A PU may containa picture header (PH) and one or more VCL NAL units composing a codedpicture.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 or provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 in the CVS, which contains one or more PPSreferring to the SPS, or provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with nuh_layer_id equal to the lowest nuh_layer_id value of thePPS NAL units that refer to the SPS NAL unit in the CVS, which containsone or more PPS referring to the SPS, or provided through externalmeans.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitor provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitin the CVS, which contains one or more PPS referring to the SPS, orprovided through external means or provided through external means.

In the same or another embodiment, pps_seq_parameter_set_id specifiesthe value of sps_seq_parameter_set_id for the referenced SPS. The valueof pps_seq_parameter_set_id may be the same in all PPSs that arereferred to by coded pictures in a CLVS.

In the same or another embodiment, all SPS NAL units with a particularvalue of sps_seq_parameter_set_id in a CVS may have the same content.

In the same or another embodiment, regardless of the nuh_layer_idvalues, SPS NAL units may share the same value space ofsps_seq_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a SPS NALunit may be equal to the lowest nuh_layer_id value of the PPS NAL unitsthat refer to the SPS NAL unit.

In an embodiment, when an SPS with nuh_layer_id equal to m is referredto by one or more PPS with nuh_layer_id equal to n. the layer withnuh_layer_id equal to m may be the same as the layer with nuh_layer_idequal to n or a (direct or indirect) reference layer of the layer withnuh_layer_id equal to m.

In an embodiment, a PPS (RBSP) shall be available to the decodingprocess prior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In the same or another embodiment, ph_pic_parameter_set_id in PHspecifies the value of pps_pic_parameter_set_id for the referenced PPSin use. The value of pps_seq_parameter_set_id may be the same in allPPSs that are referred to by coded pictures in a CLVS.

In the same or another embodiment, All PPS NAL units with a particularvalue of pps_pic_parameter_set_id within a PU shall have the samecontent.

In the same or another embodiment, regardless of the nuh_layer_idvalues, PPS NAL units may share the same value space ofpps_pic_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a PPS NALunit may be equal to the lowest nuh_layer_id value of the coded sliceNAL units that refer to the NAL unit that refer to the PPS NAL unit.

In an embodiment, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In an embodiment, a PPS (RBSP) shall be available to the decodingprocess prior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In the same or another embodiment, ph_pic_parameter_set_id in PHspecifies the value of pps_pic_parameter_set_id for the referenced PPSin use. The value of pps_seq_parameter_set_id may be the same in allPPSs that are referred to by coded pictures in a CLVS.

In the same or another embodiment, All PPS NAL units with a particularvalue of pps_pic_parameter_set_id within a PU shall have the samecontent.

In the same or another embodiment, regardless of the nuh_layer_idvalues, PPS NAL units may share the same value space ofpps_pic_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a PPS NALunit may be equal to the lowest nuh_layer_id value of the coded sliceNAL units that refer to the NAL unit that refer to the PPS NAL unit.

In an embodiment, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In an embodiment, when a flag, no_temporal_sublayer_switching_flag issignaled in a DPS, VPS, or SPS, the TemporalId value of a PPS referringto the parameter set containing the flag equal to 1 may be equal to 0,while the TemporalId value of a PPS referring to the parameter setcontaining the flag equal to 1 may be equal to or greater than theTemporalId value of the parameter set.

In an embodiment, each PPS (RBSP) may be available to the decodingprocess prior to it being referenced, included in at least one AU withTemporalId less than or equal to the TemporalId of the coded slice NALunit (or PH NAL unit) that refers it or provided through external means.When the PPS NAL unit is included in an AU prior to the AU containingthe coded slice NAL unit referring to the PPS, a VCL NAL unit enabling atemporal up-layer switching or a VCL NAL unit with nal_unit_type equalto STSA_NUT, which indicates that the picture in the VCL NAL unit may bea step-wise temporal sublayer access (STSA) picture, may not be presentsubsequent to the PPS NAL unit and prior to the coded slice NAL unitreferring to the APS.

In the same or another embodiment, the PPS NAL unit and the coded sliceNAL unit (and its PH NAL unit) referring to the PPS may be included inthe same AU.

In the same or another embodiment, the PPS NAL unit and the STSA NALunit may be included in the same AU, which is prior to the coded sliceNAL unit (and its PH NAL unit) referring to the PPS.

In the same or another embodiment, the STSA NAL unit, the PPS NAL unitand the coded slice NAL unit (and its PH NAL unit) referring to the PPSmay be present in the same AU.

In the same embodiment, the TemporalId value of the VCL NAL unitcontaining an PPS may be equal to the TemporalId value of the prior STSANAL unit.

In the same embodiment, the picture order count (POC) value of the PPSNAL unit may be equal to or greater than the POC value of the STSA NALunit.

In the same embodiment, the picture order count (POC) value of the codedslice or PH NAL unit, which refers to the PPS NAL unit, may be equal toor greater than the POC value of the referenced PPS NAL unit.

APS NAL units, Regardless of the nuh_layer_id values, may share the samevalue spaces of adaptation_parameter_set_id and aps_params_type.

The value of sps_video_parameter_set_id shall be the same in all SPSsthat are referred to by coded pictures in a CVS, across layers.

In an embodiment, in NAL unit header semantics of the current VVCspecification draft JVET-P2001 (editorially updated by JVET-Q0041), thevalue of nuh_layer_id for non-VCL NAL units is constrained as follows:If nal_unit_type is equal to PPS NUT, PREFIX_APS_NUT, or SUFFIX_APS_NUT,nuh_layer_id shall be equal to the lowest nuh_layer_id value of thecoded slice NAL units that refer to the NAL unit. Otherwise, ifnal_unit_type is equal to SPS NUT, nuh_layer_id shall be equal to thelowest nuh_layer_id value of the PPS NAL units that refer to the SPS NALunit.

The constraints are intended to allow the parameter sets (SPS, PPS, APS)reference across layers, so that a coded slice NAL unit can/shall onlyrefer to a PPS/APS NAL unit in the same or a lower layer, and a PPS NALunit can/shall only refer to a SPS NAL unit in the same or a lowerlayer. Note that a coded slice VCL NAL unit can refer to a PPS/APS NALunit in a non-reference layer, with the given constraints. For example,FIG. 22 shows a simple example 2200 with two layers, where thenuh_layer_id value of the layer B is greater than the nuh_layer_id valueof the layer A, and the layer A is not a direct/indirect reference layerof the layer B. In that case, a coded slice VCL NAL unit in the layer Bcan refer to a PPS/APS with nuh_layer_id equal to nuh_layer_id of thelayer A, because there is not a constraint to disallow a PPS/APSreference in a non-reference layer. Still, nuh_layer_id of the PPS/APSis equal to the lowest nuh_layer_id value of the coded slice NAL unitsthat refer to the NAL unit. In the example, the layer A and the layer Bmay belong to different (output) layer sets, and the NAL units of thelayer A can be discarded by a bitstream extraction process, while theNAL unit of the layer B are still present in the output bitstream. Then,the PPS/APS NAL units referred to by the coded slice NAL unit of thelayer B may not be present in the output bitstream.

In the same or another embodiment, in order to address the above issue,the current constraints need to be improved. The proposed constraint isthat a coded slice NAL unit shall only refer to a PPS/APS in the samelayer or in a (direct) reference layer, and a PPS NAL unit shall onlyrefer to a SPS in the same layer or in a (direct) reference layer. InFIG. 22, if the layer A is a reference layer of the layer B, both layersshall belong to the same (output) layer set, and shall be present in anextracted bitstream, always. Then, the SPS/PPS/APS VCL NAL unit referredto by a NAL unit in another layer are never removed.

According to embodiments, NAL unit header semantics include featuressuch that when a coded slice NAL unit refers to a non-VCL NAL unit withnal_unit_type equal to PPS_NUT, PREFIX_APS_NUT, or SUFFIX_APS_NUT, thelayer of the non-VCL NAL unit shall be equal to the layer of the codedslice NAL unit or a direct reference layer of the coded slice NAL unit,and, when a PPS NAL unit refers to an SPS NAL unit, the layer of the SPSNAL unit shall be equal to the layer of the PPS NAL unit or a directreference layer of the PPS NAL unit.

According to embodiments, NAL unit header semantics include featuressuch that when a coded slice NAL unit refers to a non-VCL NAL unit withnal_unit_type equal to PPS_NUT, PREFIX_APS_NUT, or SUFFIX_APS_NUT, thelayer of the non-VCL NAL unit shall be equal to the layer of the codedslice NAL unit or a direct/indirect reference layer of the coded sliceNAL unit, and, when a PPS NAL unit refers to an SPS NAL unit, the layerof the SPS NAL unit shall be equal to the layer of the PPS NAL unit or adirect/indirect reference layer of the PPS NAL unit.

The techniques for signaling adaptive resolution parameters describedabove, can be implemented as computer software using computer-readableinstructions and physically stored in one or more computer-readablemedia. For example, FIG. 7 shows a computer system 700 suitable forimplementing certain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 7 for computer system 700 are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 700.

Computer system 700 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 701, mouse 702, trackpad 703, touch screen 710,data-glove, joystick 705, microphone 706, scanner 707, camera 708.

Computer system 700 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 710, data-glove, or joystick 705, but there can also betactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 709, headphones (not depicted)),visual output devices (such as screens 710 to include CRT screens, LCDscreens, plasma screens, OLED screens, each with or without touch-screeninput capability, each with or without tactile feedback capability—someof which may be capable to output two dimensional visual output or morethan three dimensional output through means such as stereographicoutput; virtual-reality glasses (not depicted), holographic displays andsmoke tanks (not depicted)), and printers (not depicted).

Computer system 700 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW720 with CD/DVD or the like media 721, thumb-drive 722, removable harddrive or solid state drive 723, legacy magnetic media such as tape andfloppy disc (not depicted), specialized ROM/ASIC/PLD based devices suchas security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 700 can also include interface to one or morecommunication networks 755. Networks 755 can for example be wireless,wireline, optical. Networks 755 can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks 755 include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters 754 that attachedto certain general purpose data ports or peripheral buses (749) (suchas, for example USB ports of the computer system 700; others arecommonly integrated into the core of the computer system 700 byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem 700 can communicate with other entities. Such communication canbe uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 740 of thecomputer system 700.

The core 740 can include one or more Central Processing Units (CPU) 741,Graphics Processing Units (GPU) 742, specialized programmable processingunits in the form of Field Programmable Gate Areas (FPGA) 743, hardwareaccelerators for certain tasks 744, and so forth. These devices, alongwith Read-only memory (ROM) 745, Random-access memory 746, internal massstorage 747 such as internal non-user accessible hard drives, SSDs, andthe like, may be connected through a system bus 748. In some computersystems, the system bus 748 can be accessible in the form of one or morephysical plugs to enable extensions by additional CPUs, GPU, and thelike. The peripheral devices can be attached either directly to thecore's system bus 748, or through a peripheral bus 749. Architecturesfor a peripheral bus include PCI, USB, and the like.

CPUs 741, GPUs 742, FPGAs 743, and accelerators 744 can execute certaininstructions that, in combination, can make up the aforementionedcomputer code. That computer code can be stored in ROM 745 or RAM 746.Transitional data can be also be stored in RAM 746, whereas permanentdata can be stored for example, in the internal mass storage 747. Faststorage and retrieve to any of the memory devices can be enabled throughthe use of cache memory, that can be closely associated with one or moreCPU 741, GPU 742, mass storage 747, ROM 745, RAM 746, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 700, and specifically the core 740 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 740 that are of non-transitorynature, such as core-internal mass storage 747 or ROM 745. The softwareimplementing various embodiments of the present disclosure can be storedin such devices and executed by core 740. A computer-readable medium caninclude one or more memory devices or chips, according to particularneeds. The software can cause the core 740 and specifically theprocessors therein (including CPU, GPU, FPGA, and the like) to executeparticular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 746and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 744), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof

What is claimed is:
 1. A method of video encoding performed by at leastone processor, the method comprising: obtaining video data comprisingdata of a plurality of semantically independent source pictures;determining, among the video data, whether references are associatedwith any of a first access unit (AU) and a second AU according to atleast one picture order count (POC) signal value included with the videodata; and outputting a first quantity of the references set to the firstAU and a second quantity of the references set to the second AU based onthe at least one POC signal value, wherein determining whether thereferences are associated with any of the first AU and the second AUfurther comprises setting the first quantity of the references to thefirst AU, in response to determining that each of the first quantity ofthe references respectively comprises one of a plurality of POC valuesless than the at least one POC signal value, and wherein setting thesecond quantity of the references to the second AU, in response todetermining that each of the second quantity of the referencesrespectively comprises one of a second plurality of POC values equal toor greater than the at least one POC signal value.
 2. The methodaccording claim 1, wherein the references comprise at least one ofpictures, slices, and tiles of the video data, wherein layer IDs of anyof APS, PPS, and SPS network abstraction layer (NAL) units are lowerthan or the same as a layer ID of an NAL unit that refers to the any ofthe APS, PPS, and SPS NAL units, and wherein a layer of the any of theAPS, PPS, and SPS NAL units is a reference layer of the NAL unit.
 3. Themethod according to claim 2, wherein determining whether the referencesare associated with any of the first AU and the second AU comprisescomparing respective POC values of each of the references with the atleast one POC signal value.
 4. The method according to claim 3, whereinthe video data comprises a video parameter set (VPS) data identifying aplurality of spatial layers of the video data.
 5. The method accordingto claim 4, wherein the references comprise the slices, and wherein theat least one POC signal value is included in a slice header of the videodata.
 6. The method according to claim 4, wherein the video datacomprises a video parameter set (VPS) data identifying a plurality ofspatial layers of the video data which are shared across layers of anadaptive parameter set (APS), a picture parameter set (PPS), and asequence parameter set (SPS).
 7. The method according to claim 4,wherein the at least one POC signal value is included in the videoparameter set (VPS) of the video data.
 8. The method according to claim7, further comprising: determining whether the VPS data comprises atleast one flag indicating whether one or more of the references aredivided into a plurality of sub-regions; and determining, in a casewhere the at least one flag indicates that the one or more of thereferences are divided into the plurality of sub-regions, at least oneof, in luma samples, a full picture width and a full picture height of apicture of the one or more of the references.
 9. The method according toclaim 8, further comprising: determining, in the case where the at leastone flag indicates that the one or more of the references are dividedinto the plurality of sub-regions, a signaling value, included in asequence parameter set of the video data, specifying an offset of aportion of at least one of the sub-regions.
 10. The method according toclaim 1, wherein the plurality of semantically independent sourcepictures represent a spherical 360 picture.
 11. An apparatus for videoencoding, the apparatus comprising: at least one memory configured tostore computer program code; at least one processor configured to accessthe computer program code and operate as instructed by the computerprogram code, the computer program code including: obtaining codeconfigured to cause the at least one processor to obtain video datacomprising data of a plurality of semantically independent sourcepictures; determining code configured to cause the at least oneprocessor to determine, among the video data, whether references areassociated with any of a first access unit (AU) and a second AUaccording to at least one picture order count (POC) signal valueincluded with the video data; and outputting code configured to causethe at least one processor to output a first quantity of the referencesset to the first AU and a second quantity of the references set to thesecond AU based on the at least one POC signal value, whereindetermining whether the references are associated with any of the firstAU and the second AU further comprises setting the first quantity of thereferences to the first AU, in response to determining that each of thefirst quantity of the references respectively comprises one of aplurality of POC values less than the at least one POC signal value, andwherein setting the second quantity of the references to the second AU,in response to determining that each of the second quantity of thereferences respectively comprises one of a second plurality of POCvalues equal to or greater than the at least one POC signal value. 12.The apparatus according claim 11, wherein the references comprise atleast one of pictures, slices, and tiles of the video data, whereinlayer IDs of any of APS, PPS, and SPS network abstraction layer (NAL)units are lower than or the same as a layer ID of an NAL unit thatrefers to the any of the APS, PPS, and SPS NAL units, and wherein alayer of the any of the APS, PPS, and SPS NAL units is a reference layerof the NAL unit.
 13. The apparatus according to claim 12, whereindetermining whether the references are associated with any of the firstAU and the second AU comprises comparing respective POC values of eachof the references with the at least one POC signal value.
 14. Theapparatus according to claim 13, wherein the video data comprises avideo parameter set (VPS) data identifying a plurality of spatial layersof the video data.
 15. The apparatus according to claim 14, wherein thereferences comprise the slices, and wherein the at least one POC signalvalue is included in a slice header of the video data.
 16. The apparatusaccording to claim 14, wherein the video data comprises a videoparameter set (VPS) data identifying a plurality of spatial layers ofthe video data which are shared across layers of an adaptive parameterset (APS), a picture parameter set (PPS), and a sequence parameter set(SPS).
 17. The apparatus according to claim 14, wherein the at least onePOC signal value is included in the video parameter set (VPS) of thevideo data.
 18. The apparatus according to claim 17, wherein thedetermining code is further configured to cause the at least oneprocessor to: determine whether the VPS data comprises at least one flagindicating whether one or more of the references are divided into aplurality of sub-regions; and determine, in a case where the at leastone flag indicates that the one or more of the references are dividedinto the plurality of sub-regions, at least one of, in luma samples, afull picture width and a full picture height of a picture of the one ormore of the references.
 19. The apparatus according to claim 18, whereinthe determining code is further configured to cause the at least oneprocessor to: determine, in the case where the at least one flagindicates that the one or more of the references are divided into theplurality of sub-regions, a signaling value, included in a sequenceparameter set of the video data, specifying an offset of a portion of atleast one of the sub-regions.
 20. A non-transitory computer readablemedium storing a program configured to cause a computer to: obtain videodata comprising data of a plurality of semantically independent sourcepictures; determine, among the video data, whether references areassociated with any of a first access unit (AU) and a second AUaccording to at least one picture order count (POC) signal valueincluded with the video data; and output a first quantity of thereferences set to the first AU and a second quantity of the referencesset to the second AU based on the at least one POC signal value, whereindetermining whether the references are associated with any of the firstAU and the second AU further comprises setting the first quantity of thereferences to the first AU, in response to determining that each of thefirst quantity of the references respectively comprises one of aplurality of POC values less than the at least one POC signal value, andwherein setting the second quantity of the references to the second AU,in response to determining that each of the second quantity of thereferences respectively comprises one of a second plurality of POCvalues equal to or greater than the at least one POC signal value.